Answer:
See explanation
Step-by-step explanation:
Echo is the reflection of sound waves. Recall that ultrasound are also sound waves of high frequency.
When ultra sound meets an obstacle such as a bone, it is reflected backwards and gives rise to an echo back in the transducer.
Since ultrasound is high frequency sound wave wave; It does not passes through bone due to the high density of the bone, the data required may now be collected.